Upgrade : Proxmox VE 4.4 to Proxmox VE 5.2

  1. Upgrade latest package of Proxmox VE 4.4 release.
apt-get update && apt-get dist-upgrade

You will get this error :

W: Failed to fetch https://enterprise.proxmox.com/debian/dists/jessie/pve-enterprise/binary-amd64/Packages  HttpError401
E: Some index files failed to download. They have been ignored, or old ones used instead.

To resolved this issue just comment the content in /etc/apt/sources.list.d/pve-enterprise.list

Then run again :

apt-get update && apt-get dist-upgrade

  2. Create pve-install-repo.list

echo "deb http://download.proxmox.com/debian/pve stretch pve-no-subscription" > /etc/apt/sources.list.d/pve-install-repo.list

  3. Then run :

wget http://download.proxmox.com/debian/proxmox-ve-release-5.x.gpg -O /etc/apt/trusted.gpg.d/proxmox-ve-release-5.x.gpg

 4. Update Debian repos

sed -i 's/jessie/stretch/g' /etc/apt/sources.list

 5. Update the with new repos

apt update && apt dist-upgrade

 6. When configuring open-iscsi click YES, if not the installation may be stuck.

Done.

References:
https://pve.proxmox.com/wiki/Upgrade_from_4.x_to_5.0
https://forum.proxmox.com/threads/error-401-updating-the-system.34567/